1. Field of the Invention
The present invention relates to a process for forming an aluminum or aluminum oxide thin film and, more particularly, to a process for forming an aluminum or aluminum oxide thin film necessary to semiconductor devices.
2. Description of the Related Art
Aluminum oxide is an electrical insulator that causes visible rays to pass through. Also, aluminum oxide is a hard and strong material resistant to the attack of almost all chemicals. Aluminum oxide layers may act as a superior barrier against diffusion of many materials such as sodium. Such an aluminum oxide may be broadly used in many applications including passivation layer of semiconductor devices, gate oxide layer, insulating layer, diffusion barrier layer, dielectric layer, and the like as well as optical uses (Reference 1: Y. Kim, S. M. Lee, C. S. Park, S. I. Lee, and M. Y. Lee, Applied Physics Letters, vol. 71, p. 3604 (1997)). An extremely thin film of aluminum oxide may also be formed on the PZT (Pb(ZrTi)O3) dielectric layer of FeRAM (Ferroelectric Random Access Memory) and used as a diffusion barrier layer against penetration of hydrogen (Reference 2: Sang-Min Lee, Young-Kwan Kim, In-Sun Park, Chang-Soo Park, Cha-Young Yoo, Sang-In Lee, and Moon-Yong Lee, The Abstracts of the 5th Korean Semiconductor Academy Meeting, p 255 (1998)).
In contrast to the conventional chemical deposition method which involves simultaneous supply of sources of components constituting a thin film, sequential supply of materials allows formation of a thin film only with chemical reactions on the surface of a substrate, thus providing thickness uniformity over large areas, excellent conformality, and the growth rate of the thin film is proportional to the number of source supply cycles rather than time, as a result of which the thickness of the thin film can be controlled precisely (Reference 3: T. Suntola and M. Simpson eds. Atomic Layer Epitaxy, Blackie, London (1990)).
In the growth of aluminum oxide films using the atomic layer deposition, the source of aluminum is trichloroaluminum (AlCl3), trimethylaluminum (Al(CH3) 3) or dimethylchloroaluminum (Al(CH3) 2Cl), that of oxygen being water vapor (H2O), hydrogen peroxide (H2O2) or nitrogen monoxide (N2O) (Reference 4: Kaupo Kukli, Mikko Ritta, Markku Leskela and Janne Jokinen, J. Vac. Sci. Technol., A 15 (4), 2214 (1997)).
In the conventional atomic layer deposition, the surface reaction between aluminum and oxygen sources occurs in association with thermal decomposition reaction to grow aluminum oxide thin films so that the growth temperature has a great effect on the characteristics of the thin films, such as film composition, refractive index, dielectric constant, leakage current, and the like (Reference 5: A. W. Ott, J. W. Klaus, J. M. Johnson and S. M. George, Thin Solid Films, 292, 135 (1997)). That is, the aluminum oxide films grown at a low growth temperature have deteriorated characteristics including film composition, refractive index, dielectric constant, etc. due to contamination of the films with chlorine and carbon. On the other hand, the aluminum oxide films grown at a high growth temperature may have high refractive index and dielectric constant but deteriorated electric characteristics such as leakage current or fracture electric field.
It is, therefore, an object of the present invention to provide a process for forming aluminum or aluminum oxide thin films using aluminum and oxygen sources not contaminated with chlorine or carbon.
To achieve the above object of the present invention, there is provided a process for forming an aluminum film including the steps of: subjecting an organoaluminum compound as an aluminum source in contact with a target substrate for deposition using a carrier gas to cause a dissociation reaction of the compound; and introducing an energy source onto the substrate to form an aluminum film through a decomposition reaction (i.e. reduction) of the material adsorbed on the substrate.
In another aspect of the present invention, there is provided a process for forming an aluminum oxide film including the steps of: subjecting an organoaluminum compound as an aluminum source in contact with a target substrate for deposition using a carrier gas to cause a dissociation reaction of the compound; introducing an energy source onto the substrate to form an aluminum film through a decomposition reaction of the material adsorbed on the substrate; and introducing an oxygen-containing gas and a heat energy source to oxidize the aluminum film.
Preferably, the temperature of the substrate is maintained at less than 100xc2x0 C. for a metal substrate, and less than 150xc2x0 C. for an oxide substrate such as SiO2. Above the temperature, aluminum deposition occurs due to thermal decomposition reaction on the substrate.
The organoaluminum compound used as a deposition source is largely divided into alkyl- and alane-based sources. Examples of the alkyl-based source include triisobutyl aluminum (TIBA) and dimethyl-aluminum hydride (DMAH). Examples of the alane-based source include trimethyl-amine alane (TMAA), triethylamine alane (TEAA), and dimethylethyl-amine alane (DMEAA). The alane-based source is a compound in which amine as a nitrogen compound is coordinated with alane bonded to three hydrogens and free from Alxe2x80x94C bonds, as a result of which a high-purity thin film can be obtained. Preferably, use is made of an amine-alane-based source in which a nitrogen compound, i.e., amine has a weak bond to alane having three hydrogens associated with aluminum. More preferably, the organoaluminum compound is DMEAA.
Preferably, the carrier gas is any one selected from the group consisting of hydrogen, argon, helium, and nitrogen. More preferably, the carrier gas is hydrogen. The hydrogen atmosphere in the reactor not only stabilizes the Alxe2x80x94N bond in the gaseous phase but also prevents leaving of alane from hydrogen, thus stabilizing the alane.
The energy source used for reduction of alane adsorbed to the surface of the substrate to deposit aluminum is heat energy, plasma energy, light energy (e.g., laser, ultraviolet rays, infrared rays, etc.), and the like. For plasma energy, argon, helium or hydrogen plasma may be used. Hydrogen plasma is preferable, because the hydrogen atmosphere stabilizes the Alxe2x80x94N bond in the gaseous phase and inhibits gas dissociation of DMEAA.
The number of times of aluminum deposition prior to the oxidization step (i.e., the number of aluminum films to be deposited) is optionally controllable. That is, the step of oxidization after n times of aluminum deposition is repeated to deposit multi-layered aluminum oxide films.
Besides, the deposition time period, i.e., injection time of the aluminum source, injection time period of a purging gas, and time period for applying plasma energy can also be controlled.
As for the energy source required to oxidize the laminated aluminum film, a gas such as vapor (H2O), hydrogen peroxide (H2O2), nitrogen monoxide (N2O), oxygen (O2), or ozone (O3) is used to supply heat energy, light energy (e.g., laser, ultraviolet rays, infrared rays, etc.) or plasma energy.
The plasma oxidization method is preferably used in oxidization of the laminated aluminum thin film, in which the plasma gas is an oxygen-containing gas and preferably contains high-purity oxygen.